Display device and method for fabricating the same

ABSTRACT

A display device comprises a substrate, a pixel electrode on the substrate, a light emitting element on the pixel electrode, and a common electrode layer on the light emitting element, and configured to receive a common voltage, wherein the light emitting element configured to emit a first light according to a driving current having a first current density, is configured to emit a second light according to a driving current having a second current density, and is configured to emit a third light according to a driving current having a third current density.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to, and the benefit of, Korean PatentApplication No. 10-2021-0135740 filed on Oct. 13, 2021, in the KoreanIntellectual Property Office (KIPO), the entire content of which isincorporated by reference herein.

BACKGROUND 1. Field

The present disclosure relates to a display device and a method forfabricating the same.

2. Description of the Related Art

With the advance of information-oriented society, more and more demandsare placed on display devices for displaying images in various ways. Thedisplay device may be a flat panel display device, such as a liquidcrystal display, a field emission display, and a light emitting display.A light emitting display device may include an organic light emittingdisplay device including an organic light emitting diode element as alight emitting element, an inorganic light emitting display deviceincluding an inorganic semiconductor element as a light emittingelement, or a micro light emitting display device an ultra-small lightemitting diode element (or micro light emitting diode element) as alight emitting element.

Recently, a head mounted display including the light emitting displaydevice has been developed. A head mounted display (HMD) is aglasses-type monitor device of virtual reality (VR) or augmented realitythat is worn in the form of glasses or a helmet to form a focus at adistance close to the user's eyes.

A high-resolution micro light emitting diode display including a microlight emitting diode element is applied to the head mounted display.When the micro light emitting diode element emits a single color, awavelength conversion layer for converting the wavelength of lightemitted from the micro light emitting diode element is essential inorder to allow the micro light emitting diode display to display variouscolors.

SUMMARY

Aspects of embodiments of the present disclosure include a micro lightemitting diode element that emits light of a red wavelength band, amicro light emitting diode element that emits light of a greenwavelength band, and a micro light emitting diode element that emitslight of a blue wavelength band, and thus does not require a wavelengthconversion layer, and a method for fabricating the micro light emittingdiode and/or a display device including the same.

However, embodiments of the present disclosure are not limited to thoseset forth herein. The above and other embodiments of the presentdisclosure will become more apparent to one of ordinary skill in the artto which the present disclosure pertains by referencing the detaileddescription of the present disclosure given below.

According to one or more embodiments of the present disclosure, there isprovided a display device including a substrate, a pixel electrode onthe substrate, a light emitting element on the pixel electrode, and acommon electrode layer on the light emitting element, and configured toreceive a common voltage, wherein the light emitting element configuredto emit a first light according to a driving current having a firstcurrent density, is configured to emit a second light according to adriving current having a second current density, and is configured toemit a third light according to a driving current having a third currentdensity.

One frame period may include a first period, a second period, and athird period, wherein the driving current is applied at the firstcurrent density during the first period, is applied at the secondcurrent density during the second period, and is applied at the thirdcurrent density during the third period.

When the light emitting element emits light with a peak white grayscale,a length of the first period may be longer than a length of the secondperiod, and the length of the second period may be longer than a lengthof the third period.

The first current density may be less than the second current density,wherein the first light has a longer wavelength than the second light.

The second current density may be less than the third current density,wherein the second light has a longer wavelength than the third light.

The first light may be light of a red wavelength band, the second lightmay be light of a green wavelength band, and the third light may belight of a blue wavelength band.

An active layer of the light emitting element may include InGaN havingan indium (In) content of about 30% to about 45%.

A first peak current value of the driving current during the firstperiod may be lower than a second peak current value of the drivingcurrent during the second period.

A second peak current value of the driving current during the secondperiod may be lower than a third peak current value of the drivingcurrent during the third period.

The first current density of the driving current may be constant duringthe first period, the second current density of the driving current maybe constant during the second period, and the third current density ofthe driving current may be constant during the third period.

The first period, the second period, and the third period may beadjusted according to a grayscale of the light emitting element.

One frame period may include R (R being an integer greater than or equalto 2) first periods, Q (Q being an integer greater than or equal to 2)second periods, and P (P being an integer greater than or equal to 2)third periods, wherein the driving current is applied at the firstcurrent density during the first periods, is applied at the secondcurrent density during the second periods, and is applied at the thirdcurrent density during the third periods.

In the one frame period, a sum of the first periods may be longer than asum of the second periods, and the sum of the second periods may belonger than a sum of the third periods.

According to one or more embodiments of the present disclosure, there isprovided a display device including a substrate, pixel electrodes on thesubstrate, light emitting elements respectively on the pixel electrodes,and a common electrode layer on the light emitting elements, andconfigured to receive a common voltage, wherein each of the lightemitting elements includes a first light emitting element configured toemit a first light according to a first driving current having a firstcurrent density, and configured to emit a second light according to afirst driving current having a second current density, and a secondlight emitting element configured to emit a third light according to asecond driving current.

One frame period may include a first period and a second period, whereinthe driving current is configured to be applied at the first currentdensity during the first period, and is configured to be applied at thesecond current density during the second period.

When the first light emitting element emits light with a peak luminance,a length of the first period may be longer than a length of the secondperiod.

The first current density may be less than the second current density,and the first light may have a longer wavelength than the second light.

An area of the first light emitting element may be larger than an areaof the second light emitting element.

An active layer of the first light emitting element may include InGaNhaving an indium (In) content of about 30% to about 45%, wherein anactive layer of the second light emitting element includes InGaN havingan indium (In) content of 10% to 20%.

According to one or more embodiments of the present disclosure, there isprovided a method for fabricating a display device, the method includingforming a common electrode layer on a substrate, forming a hard mask onthe common electrode layer, etching the hard mask to form openingsexposing the common electrode layer, forming light emitting elements inthe openings, respectively, removing the hard mask, forming firstconnection electrodes on the light emitting elements, respectively,forming second connection electrodes on pixel electrodes of asemiconductor circuit board, respectively, and bonding the firstconnection electrodes to the second connection electrodes, wherein anactive layer of each of the light emitting elements includes InGaNhaving an indium (In) content of about 30% to about 45%.

According to one or more embodiments of the present disclosure, there isprovided a method for fabricating a display device, the method includingforming a common electrode layer on a substrate, forming a hard mask onthe common electrode layer, etching the hard mask to form first openingsexposing the common electrode layer, forming first light emittingelements in the first openings, respectively, forming a mask patterncovering the first light emitting elements, etching the mask pattern toform second openings exposing the common electrode layer, and formingsecond light emitting elements in the second openings, respectively,wherein an active layer of the first light emitting element includesInGaN having an indium (In) content of about 30% to about 45%, andwherein an active layer of the second light emitting element includesInGaN having an indium (In) content of 10% to 20%.

According to the aforementioned and other embodiments of the presentdisclosure, each of a plurality of pixels of a display panel may includea light emitting element that emits any one of first light, secondlight, and third light depending on a current density, so that variouscolors may be displayed without the wavelength conversion layer.

According to the aforementioned and other embodiments of the presentdisclosure, when the light emitting layer of a light emitting element ismade of InGaN having an indium content of about 30% to about 45%, thedriving current applied to the light emitting layer is time-divided andapplied to the light emitting element, so that the light emittingelement may perform time division to emit the first light, the secondlight, and the third light.

According to the aforementioned and other embodiments of the presentdisclosure, a pixel includes a light emitting element that emits any oneof the first light, the second light, and the third light depending on acurrent density. Accordingly, it is possible to simplify a manufacturingprocess and reduce a manufacturing cost compared to the case ofseparately forming first light emitting elements that emit the firstlight, second light emitting elements and fourth light emitting elementsthat emit the second light, and third light emitting elements that emitthe third light.

According to the aforementioned and other embodiments of the presentdisclosure, each of the plurality of pixels of the display panelincludes a first light emitting element that emits any one of firstlight and second light depending on the current density, and a secondlight emitting element that emits third light, so that various colorsmay be displayed without the wavelength conversion layer.

According to the aforementioned and other embodiments of the presentdisclosure, when the first light emitting layer of the first lightemitting element is made of InGaN having an indium content of about 30%to about 45%, a first driving current applied to the first lightemitting layer is time-divided and applied to the first light emittingelement, so that the first light emitting element may perform timedivision to emit the first light and the second light.

According to the aforementioned and other embodiments of the presentdisclosure, a pixel includes the first light emitting element that emitsany one of the first light and the second light depending on the currentdensity, and the second light emitting element that emits the thirdlight. Accordingly, it is possible to simplify the manufacturing processand reduce the manufacturing cost compared to the case of separatelyforming the first light emitting elements that emit the first light, thesecond light emitting elements and the fourth light emitting elementsthat emit the second light, and the third light emitting elements thatemit the third light.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other embodiments of the present disclosure will becomemore apparent by describing embodiments thereof with reference to theattached drawings, in which:

FIG. 1 is a perspective view illustrating a display device according toone or more embodiments;

FIG. 2 is a layout diagram showing in detail an example of area A ofFIG. 1 ;

FIG. 3 is a cross-sectional view illustrating an example of a displaypanel taken along line A-A′ of FIG. 2 ;

FIG. 4 is a diagram illustrating the band gap of the active layer of alight emitting element in the case of applying a driving current havinga first current density;

FIG. 5 is a diagram illustrating the band gap of the active layer of alight emitting element in the case of applying a driving current havinga second current density;

FIG. 6 is a waveform diagram illustrating a driving current according toone or more embodiments;

FIG. 7 is a waveform diagram illustrating a driving current applied to alight emitting element according to one or more other embodiments;

FIG. 8 is a flowchart illustrating a method for fabricating a displaydevice according to one or more embodiments;

FIGS. 9 to 15 are cross-sectional views illustrating a method forfabricating a display device according to one or more embodiments;

FIG. 16A is a layout diagram illustrating another example of area A ofFIG. 1 ;

FIG. 16B is a layout diagram illustrating still another example of areaA of FIG. 1 ;

FIG. 17 is a cross-sectional view illustrating an example of a displaypanel taken along line B-B′ of FIG. 16A;

FIG. 18 is a waveform diagram illustrating a first driving current and asecond driving current according to one or more embodiments;

FIG. 19 is a waveform diagram illustrating a first driving current and asecond driving current according to one or more other embodiments;

FIG. 20 is a flowchart illustrating a method for fabricating a displaydevice according to still one or more other embodiments;

FIGS. 21 to 28 are cross-sectional views illustrating a method forfabricating a display device according to one or more embodiments;

FIG. 29 is a diagram illustrating a virtual reality device including adisplay device according to one or more embodiments;

FIG. 30 is a diagram illustrating a smart device including a displaydevice according to one or more embodiments;

FIG. 31 is a view illustrating a dashboard of an automobile and a centerfascia including a display device according to one or more embodiments;and

FIG. 32 is a diagram illustrating a transparent display device includinga display device according to one or more embodiments.

DETAILED DESCRIPTION

Aspects of some embodiments of the present disclosure and methods ofaccomplishing the same may be understood more readily by reference tothe detailed description of embodiments and the accompanying drawings.Hereinafter, embodiments will be described in more detail with referenceto the accompanying drawings. The described embodiments, however, may beembodied in various different forms, and should not be construed asbeing limited to only the illustrated embodiments herein. Rather, theseembodiments are provided as examples so that this disclosure will bethorough and complete, and will fully convey the aspects of embodimentsof the present disclosure to those skilled in the art. Accordingly,processes, elements, and techniques that are not necessary to thosehaving ordinary skill in the art for a complete understanding of theaspects of embodiments of the present disclosure might not be described.

Unless otherwise noted, like reference numerals, characters, orcombinations thereof denote like elements throughout the attacheddrawings and the written description, and thus, descriptions thereofwill not be repeated. Further, parts not related to the description ofsome embodiments might not be shown to make the description clear.

In the drawings, the relative sizes of elements, layers, and regions maybe exaggerated for clarity. Additionally, the use of cross-hatchingand/or shading in the accompanying drawings is generally provided toclarify boundaries between adjacent elements. As such, neither thepresence nor the absence of cross-hatching or shading conveys orindicates any preference or requirement for particular materials,material properties, dimensions, proportions, commonalities betweenillustrated elements, and/or any other characteristic, attribute,property, etc., of the elements, unless specified.

Various embodiments are described herein with reference to sectionalillustrations that are schematic illustrations of embodiments and/orintermediate structures. As such, variations from the shapes of theillustrations as a result, for example, of manufacturing techniquesand/or tolerances, are to be expected. Further, specific structural orfunctional descriptions disclosed herein are merely illustrative for thepurpose of describing embodiments according to the concept as well asaspects of embodiments of the present disclosure. Thus, embodimentsdisclosed herein should not be construed as limited to the particularillustrated shapes of regions, but are to include deviations in shapesthat result from, for instance, manufacturing.

For example, an implanted region illustrated as a rectangle will,typically, have rounded or curved features and/or a gradient of implantconcentration at its edges rather than a binary change from implanted tonon-implanted region. Likewise, a buried region formed by implantationmay result in some implantation in the region between the buried regionand the surface through which the implantation takes place. Thus, theregions illustrated in the drawings are schematic in nature and theirshapes are not intended to illustrate the actual shape of a region of adevice and are not intended to be limiting. Additionally, as thoseskilled in the art would realize, the described embodiments may bemodified in various different ways, all without departing from thespirit or scope of the present disclosure.

In the detailed description, for the purposes of explanation, numerousspecific details are set forth to provide a thorough understanding ofvarious embodiments. It is apparent, however, that various embodimentsmay be practiced without these specific details or with one or moreequivalent arrangements. In other instances, well-known structures anddevices are shown in block diagram form in order to avoid unnecessarilyobscuring various embodiments.

Spatially relative terms, such as “beneath,” “below,” “lower,” “under,”“above,” “upper,” and the like, may be used herein for ease ofexplanation to describe one element's or feature's relationship toanother element(s) or feature(s) as illustrated in the figures. It willbe understood that the spatially relative terms are intended toencompass different orientations of the device in use or in operation,in addition to the orientation depicted in the figures. For example, ifthe device in the figures is turned over, elements described as “below”or “beneath” or “under” other elements or features would then beoriented “above” the other elements or features. Thus, the example terms“below” and “under” can encompass both an orientation of above andbelow. The device may be otherwise oriented (e.g., rotated 90 degrees orat other orientations) and the spatially relative descriptors usedherein should be interpreted accordingly. Similarly, when a first partis described as being arranged “on” a second part, this indicates thatthe first part is arranged at an upper side or a lower side of thesecond part without the limitation to the upper side thereof on thebasis of the gravity direction.

Further, in this specification, the phrase “on a plane,” or “a planview,” means viewing a target portion from the top, and the phrase “on across-section” means viewing a cross-section formed by verticallycutting a target portion from the side.

It will be understood that when an element, layer, region, or componentis referred to as being “formed on,” “on,” “connected to,” or “coupledto” another element, layer, region, or component, it can be directlyformed on, on, connected to, or coupled to the other element, layer,region, or component, or indirectly formed on, on, connected to, orcoupled to the other element, layer, region, or component such that oneor more intervening elements, layers, regions, or components may bepresent. For example, when a layer, region, or component is referred toas being “electrically connected” or “electrically coupled” to anotherlayer, region, or component, it can be directly electrically connectedor coupled to the other layer, region, and/or component or interveninglayers, regions, or components may be present. However, “directlyconnected/directly coupled” refers to one component directly connectingor coupling another component without an intermediate component. Otherexpressions describing relationships between components such as“between,” “immediately between” or “adjacent to” and “directly adjacentto” may be construed similarly. In addition, it will also be understoodthat when an element or layer is referred to as being “between” twoelements or layers, it can be the only element or layer between the twoelements or layers, or one or more intervening elements or layers mayalso be present.

For the purposes of this disclosure, expressions such as “at least oneof,” when preceding a list of elements, modify the entire list ofelements and do not modify the individual elements of the list. Forexample, “at least one of X, Y, and Z,” “at least one of X, Y, or Z,”and “at least one selected from the group consisting of X, Y, and Z” maybe construed as X only, Y only, Z only, any combination of two or moreof X, Y, and Z, such as, for instance, XYZ, XYY, YZ, and ZZ, or anyvariation thereof. Similarly, the expression such as “at least one of Aand B” may include A, B, or A and B. As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items. For example, the expression such as “A and/or B” mayinclude A, B, or A and B.

It will be understood that, although the terms “first,” “second,”“third,” etc., may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are used to distinguish one element, component, region,layer or section from another element, component, region, layer orsection. Thus, a first element, component, region, layer or sectiondescribed below could be termed a second element, component, region,layer or section, without departing from the spirit and scope of thepresent disclosure.

In the examples, the x-axis, the y-axis, and/or the z-axis are notlimited to three axes of a rectangular coordinate system, and may beinterpreted in a broader sense. For example, the x-axis, the y-axis, andthe z-axis may be perpendicular to one another, or may representdifferent directions that are not perpendicular to one another. The sameapplies for first, second, and/or third directions.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a” and “an” are intendedto include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising,” “have,” “having,” “includes,” and“including,” when used in this specification, specify the presence ofthe stated features, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof.

As used herein, the term “substantially,” “about,” “approximately,” andsimilar terms are used as terms of approximation and not as terms ofdegree, and are intended to account for the inherent deviations inmeasured or calculated values that would be recognized by those ofordinary skill in the art. “About” or “approximately,” as used herein,is inclusive of the stated value and means within an acceptable range ofdeviation for the particular value as determined by one of ordinaryskill in the art, considering the measurement in question and the errorassociated with measurement of the particular quantity (i.e., thelimitations of the measurement system). For example, “about” may meanwithin one or more standard deviations, or within ±30%, 20%, 10%, 5% ofthe stated value. Further, the use of “may” when describing embodimentsof the present disclosure refers to “one or more embodiments of thepresent disclosure.”

When one or more embodiments may be implemented differently, a specificprocess order may be performed differently from the described order. Forexample, two consecutively described processes may be performedsubstantially at the same time or performed in an order opposite to thedescribed order.

Also, any numerical range disclosed and/or recited herein is intended toinclude all sub-ranges of the same numerical precision subsumed withinthe recited range. For example, a range of “1.0 to 10.0” is intended toinclude all subranges between (and including) the recited minimum valueof 1.0 and the recited maximum value of 10.0, that is, having a minimumvalue equal to or greater than 1.0 and a maximum value equal to or lessthan 10.0, such as, for example, 2.4 to 7.6. Any maximum numericallimitation recited herein is intended to include all lower numericallimitations subsumed therein, and any minimum numerical limitationrecited in this specification is intended to include all highernumerical limitations subsumed therein. Accordingly, Applicant reservesthe right to amend this specification, including the claims, toexpressly recite any sub-range subsumed within the ranges expresslyrecited herein. All such ranges are intended to be inherently describedin this specification such that amending to expressly recite any suchsubranges would comply with the requirements of 35 U.S.C. § 112(a) and35 U.S.C. § 132(a).

The electronic or electric devices and/or any other relevant devices orcomponents according to one or more embodiments of the presentdisclosure described herein may be implemented utilizing any suitablehardware, firmware (e.g. an application-specific integrated circuit),software, or a combination of software, firmware, and hardware. Forexample, the various components of these devices may be formed on oneintegrated circuit (IC) chip or on separate IC chips. Further, thevarious components of these devices may be implemented on a flexibleprinted circuit film, a tape carrier package (TCP), a printed circuitboard (PCB), or formed on one substrate.

Further, the various components of these devices may be a process orthread, running on one or more processors, in one or more computingdevices, executing computer program instructions and interacting withother system components for performing the various functionalitiesdescribed herein. The computer program instructions are stored in amemory which may be implemented in a computing device using a standardmemory device, such as, for example, a random access memory (RAM). Thecomputer program instructions may also be stored in other non-transitorycomputer readable media such as, for example, a CD-ROM, flash drive, orthe like. Also, a person of skill in the art should recognize that thefunctionality of various computing devices may be combined or integratedinto a single computing device, or the functionality of a particularcomputing device may be distributed across one or more other computingdevices without departing from the spirit and scope of the presentdisclosure.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which the present disclosure belongs. Itwill be further understood that terms, such as those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and/orthe present specification, and should not be interpreted in an idealizedor overly formal sense, unless expressly so defined herein.

FIG. 1 is a perspective view illustrating a display device according toone or more embodiments. FIG. 2 is a layout diagram showing in detail anexample of area A of FIG. 1 .

Although FIGS. 1 and 2 have mainly described the case where a displaydevice according to one or more embodiments is a micro light emittingdiode display device (e.g., micro or nano light emitting diode displaydevice) including a micro light emitting diode (e.g., micro or nanolight emitting diode) as a light emitting element, the presentdisclosure is not limited thereto.

In addition, in FIGS. 1 and 2 , the display device according to one ormore embodiments is mainly described as being a light emitting diode onsilicon (LEDoS) in which light emitting diodes (LED) are located aslight emitting elements on a semiconductor circuit board 101 (e.g., seeFIG. 3 ) formed by a semiconductor process using a silicon wafer, but itshould be noted that the present disclosure is not limited thereto.

Further, in FIGS. 1 and 2 , a first direction DR1 indicates a horizontaldirection of a display panel 100, a second direction DR2 indicates avertical direction of the display panel 100, and a third direction DR3indicates a thickness direction of the display panel 100 or a thicknessdirection of the semiconductor circuit board 101. In this case, “left,”“right,” “upper,” and “lower” indicate directions when the display panel100 is viewed from above. For example, “right side” indicates one sideof the first direction DR1, “left side” indicates the other side of thefirst direction DR1, “upper side” indicates one side of the seconddirection DR2, and “lower side” indicates the other side of the seconddirection DR2. Further, “upper portion” indicates one side of the thirddirection DR3, and “lower portion” indicates the other side of the thirddirection DR3.

Referring to FIGS. 1 and 2 , the display device 10 according to one ormore embodiments includes the display panel 100 including a display areaDA and a non-display area NDA.

The display panel 100 may have a quadrilateral planar shape having longsides in the first direction DR1 and short sides in the second directionDR2. However, the planar shape of the display panel 100 is not limitedthereto, and may have a polygonal shape other than a quadrilateralshape, a circular shape, an elliptical shape, or an atypical shape.

The display area DA may be an area where an image is displayed, and thenon-display area NDA may be an area where an image is not displayed. Theplanar shape of the display area DA may follow the planar shape of thedisplay panel 100. FIG. 1 illustrates that the planar shape of thedisplay area DA is a quadrilateral shape. The display area DA may begenerally located at the central area of the display panel 100. Thenon-display area NDA may be located around the display area DA. Thenon-display area NDA may be located to surround the display area DA.

The display area DA of the display panel 100 may include a plurality ofpixels PX. In the display area DA, the plurality of pixels PX may bearranged in the first direction DR1 and the second direction DR2. Thatis, the plurality of pixels PX may be arranged in a matrix.

The pixel PX may include one light emitting element LE. The pixel PX maybe defined as a minimum light emitting unit capable of displaying whitelight by combining lights emitted from the light emitting element LE.

The light emitting element LE may emit the first light, the secondlight, and the third light depending on the current density of thedriving current applied thereto. The first light may be light of a redwavelength band, the second light may be light of a green wavelengthband, and the third light may be light of a blue wavelength band. Forexample, the main peak wavelength (R-peak) of the first light may bewithin a range of about 600 nm to about 750 nm, the main peak wavelength(G-peak) of the second light may be within a range of about 480 nm toabout 560 nm, and the main peak wavelength (B-peak) of the third lightmay be within a range of about 370 nm to about 460 nm, but the presentdisclosure is not limited thereto.

The light emitting element LE may have a circular planar shape as shownin FIG. 2 , but the present disclosure is not limited thereto. Forexample, the light emitting element LE may have a polygonal shape, suchas a triangular shape, a quadrilateral shape, a pentagonal shape, ahexagonal shape, and an octagonal shape, an elliptical shape, or anatypical shape.

The non-display area NDA may include a first common voltage supply areaCVA1, a second common voltage supply area CVA2, a first pad area PDA1, asecond pad area PDA2, and a peripheral area PHA.

The first common voltage supply area CVA1 may be located between thefirst pad area PDA1 and the display area DA. The second common voltagesupply area CVA2 may be located between the second pad area PDA2 and thedisplay area DA. Each of the first common voltage supply area CVA1 andthe second common voltage supply area CVA2 may include a plurality ofcommon electrode connection portions CVS connected to a common electrodelayer CEL (see FIG. 9 ). A common voltage may be supplied to the commonelectrode layer CEL through the plurality of common electrode connectionportions CVS.

The plurality of common electrode connection portions CVS of the firstcommon voltage supply area CVA1 may be electrically connected to any oneof first pads of the first pad area PDA1. That is, the plurality ofcommon electrode connection portions CVS of the first common voltagesupply area CVA1 may receive a common voltage from any one of the firstpads of the first pad area PDA1.

The plurality of common electrode connection portions CVS of the secondcommon voltage supply area CVA2 may be electrically connected to any oneof second pads of the second pad area PDA2. That is, the plurality ofcommon electrode connection portions CVS of the second common voltagesupply area CVA2 may receive a common voltage from any one of the secondpads of the second pad area PDA2.

The first pad area PDA1 may be located on the upper side of the displaypanel 100. The first pad area PDA1 may include the first pads to beconnected to an external circuit board.

The second pad area PDA2 may be located on the lower side of the displaypanel 100. The second pad area PDA2 may include the second pads to beconnected to the external circuit board. The second pad area PDA2 may beomitted in other embodiments.

The peripheral area PHA may be the area not including the first commonvoltage supply area CVA1, the second common voltage supply area CVA2,the first pad area PDA1, and the second pad area PDA2 in the non-displayarea NDA. The peripheral area PHA may be located to surround not onlythe display area DA, but also the first common voltage supply area CVA1,the second common voltage supply area CVA2, the first pad area PDA1, andthe second pad area PDA2.

FIG. 3 is a cross-sectional view illustrating an example of a displaypanel taken along line A-A′ of FIG. 2 .

Referring to FIG. 3 , the display panel 100 according to one or moreembodiments may include the semiconductor circuit board 101 and a lightemitting element layer 200.

The semiconductor circuit board 101 may include a first substrate 110, aplurality of pixel circuit units PXC, pixel electrodes AE, the commonelectrode connection portion CVS, and the first pad PD1.

The first substrate 110 may be a silicon wafer substrate. The firstsubstrate 110 may be made of monocrystalline silicon.

Each of the plurality of pixel circuit units PXC may be located on thefirst substrate 110. Each of the plurality of pixel circuit units PXCmay include a complementary metal-oxide semiconductor (CMOS) circuitformed by the semiconductor process. Each of the plurality of pixelcircuit units PXC may include at least one transistor formed by thesemiconductor process. Further, each of the plurality of pixel circuitunits PXC may further include at least one capacitor formed by thesemiconductor process.

The plurality of pixel circuit units PXC may be located in the displayarea DA. Among the plurality of pixel circuit units PXC, each of thepixel circuit units PXC located in the display area DA may beelectrically connected to a pixel electrode AE corresponding thereto.That is, the plurality of pixel circuit units PXC and the plurality ofpixel electrodes AE may be connected in a one-to-one correspondence.Each of the plurality of pixel circuit units PXC may apply a pixelvoltage to the respective pixel electrode AE.

The plurality of pixel electrodes AE may be located in the display areaDA. Each of the plurality of pixel electrodes AE may be located on apixel circuit unit PXC corresponding thereto. Each of the pixelelectrodes AE may be an exposed electrode that is formed integrally withthe pixel circuit unit PXC and exposed from the pixel circuit unit PXC.That is, each of the pixel electrodes AE may protrude from the topsurface of the pixel circuit unit PXC. Each of the pixel electrodes AEmay receive a pixel voltage from the pixel circuit unit PXC. The pixelelectrodes AE may contain a metal material such as aluminum (Al).

The plurality of common electrode connection portions CVS may be locatedin common electrode areas CPA1 and CPA2 of the non-display area NDA.Each of the plurality of common electrode connection portions CVS may belocated on a pixel circuit unit PXC corresponding thereto. The commonelectrode connection portion CVS may be an exposed electrode integrallyformed with the pixel circuit unit PXC and exposed from the pixelcircuit unit PXC. That is, each of the common electrode connectionportions CVS may protrude from the top surface of the pixel circuit unitPXC. The common electrode connection portion CVS may contain a metalmaterial such as aluminum (Al).

The plurality of first pads PD1 may be located in the first pad areaPDA1 of the non-display area NDA. Each of the plurality of first padsPD1 may be connected to a circuit pad CPD1 of a circuit board 700through a conductive connection member, such as a wire WR. That is, thefirst pad PD1 and the circuit pad CPD1 of the circuit board 700 may beelectrically connected to each other through the wire WR.

In one or more embodiments, the semiconductor circuit board 101 and thecircuit board 700 may be located on a separate lower substrate. Thesemiconductor circuit board 101 and the circuit board 700 may beattached to the top surface of the lower substrate using an adhesivemember such as a pressure sensitive adhesive.

The circuit board 700 may be a flexible printed circuit board (FPCB), aprinted circuit board (PCB), a flexible printed circuit (FPC), or aflexible film such as a chip on film (COF).

The light emitting element layer 200 may include light emitting elementsLE, the common electrode layer CEL, and connection electrodes CNE1 andCNE2.

Each of the light emitting elements LE may be located on a pixelelectrode AE corresponding thereto. Each of the light emitting elementsLE may extend in the third direction DR3 (e.g., the thickness directionof the first substrate 110). The length of each of the light emittingelements LE in the third direction DR3 may be longer than the lengththereof in the horizontal direction. The length in the horizontaldirection may be the length in the first direction DR1 or the seconddirection DR2. For example, the length of each of the light emittingelements LE in the third direction DR3 may be about 1 μm to about 5 μm.Each of the light emitting elements LE may have a cylindrical shape thatis greater in width than in height, a disc shape, or a rod shape.However, the present disclosure is not limited thereto, and each of thelight emitting elements LE may have various shapes, such as a rod shape,a wire shape, a tube shape, a polygonal prism shape such as a regularcube, a rectangular parallelepiped, and a hexagonal prism, or a shapeextending in one direction and having a partially inclined outersurface.

In accordance with one or more embodiments, each of the light emittingelements LE may include a first semiconductor layer SEM1, an electronblocking layer EBL, an active layer MQW, a superlattice layer SLT, and asecond semiconductor layer SEM2. The first semiconductor layer SEM1, theelectron blocking layer EBL, the active layer MQW, the superlatticelayer SLT, and the second semiconductor layer SEM2 may be sequentiallystacked in the third direction DR3.

The first semiconductor layer SEM1 may be a p-type semiconductor, andmay include a semiconductor material having a chemical formula ofAlxGayIn1−x−yN (0≤x≤1, 0≤y≤1, 0≤x+y≤1). For example, it may be any oneor more of p-type doped AlGaInN, GaN, AlGaN, InGaN, AlN, and InN. Thefirst semiconductor layer SEM1 may be doped with a p-type dopant, andthe p-type dopant may be Mg, Zn, Ca, Ba, or the like. For example, thefirst semiconductor layer SEM1 may be p-GaN doped with p-type Mg. Thefirst semiconductor layer SEM1 may have a thickness within a range ofabout 30 nm to about 200 nm.

The electron blocking layer EBL may be located on the firstsemiconductor layer SEM1. The electron blocking layer EBL may reduce orprevent electrons flowing into the active layer MQW from being injectedinto another layer without being recombined with holes in the activelayer MQW. For example, the electron blocking layer EBL may be p-AlGaNdoped with p-type Mg. The thickness of the electron blocking layer EBLmay be within a range of about 10 nm to about 50 nm, but the presentdisclosure is not limited thereto. In some embodiments, the electronblocking layer EBL may be omitted.

The active layer MQW may be located on the electron blocking layer EBL.The active layer MQW may emit light due to recombination of theelectrons and the holes in response to the light emitting signal appliedthrough the first semiconductor layer SEM1 and the second semiconductorlayer SEM2. The active layer MQW may include a material having a singleor multiple quantum well structure. When the active layer MQW includes amaterial having a multiple quantum well structure, the active layer MQWmay have a quantum well structure in which a plurality of well layersand barrier layers are alternately stacked. At this time, the well layermay be formed of InGaN, and the barrier layer may be formed of GaN orAlGaN, but the present disclosure is not limited thereto. For example,the active layer MQW may have a structure in which semiconductormaterials having large band gap energy and semiconductor materialshaving small band gap energy are alternately stacked, and may includeother group III to V semiconductor materials according to the wavelengthband of the emitted light.

The superlattice layer SLT is located on the active layer MQW. Thesuperlattice layer SLT may reduce stress due to the difference inlattice constant between the second semiconductor layer SEM2 and theactive layer MQW. For example, the superlattice layer SLT may be formedof InGaN or GaN. The thickness of the superlattice layer SLT may beabout 50 nm to about 200 nm. However, the superlattice layer SLT may beomitted.

The second semiconductor layer SEM2 may be located on the superlatticelayer SLT. The second semiconductor layer SEM2 may be an n-typesemiconductor. The second semiconductor layer SEM2 may include asemiconductor material having a chemical formula of AlxGayIn1−x−yN(0≤x≤1, 0≤y≤1, 0≤x+y≤1). For example, it may be any one or more ofn-type doped AlGaInN, GaN, AlGaN, InGaN, AlN, and InN. The secondsemiconductor layer SEM2 may be doped with an n-type dopant, and then-type dopant may be Si, Ge, Sn, or the like. For example, the secondsemiconductor layer SEM2 may be n-GaN doped with n-type Si. Thethickness of the second semiconductor layer SEM2 may be within a rangeof about 500 nm to about 1 μm, but the present disclosure is not limitedthereto.

In accordance with one or more embodiments, when the active layer MQW ofeach of the light emitting elements LE is made of InGaN, the color ofthe light emitted from the active layer MQW may vary depending on thecontent of indium (In). For example, as the content of indium (In)increases, the wavelength band of the light emitted from the activelayer MQW may be shifted to a red wavelength band, and as the content ofindium (In) decreases, the wavelength band of the light emitted from theactive layer MQW may be shifted to a blue wavelength band. The contentof indium (In) in the active layer MQW may be about 30% to about 45%. Inthis case, when a driving current having a high current density isapplied, the active layer MQW may emit light of a short wavelength(e.g., the third light). When a driving current having a low currentdensity is applied, the active layer MQW may emit light of a longwavelength (e.g., the first light). That is, the active layer MQW mayemit any one of the first light, the second light, and the third lightdepending on the current density of the driving current.

Although FIG. 3 illustrates that each of the light emitting elements LEhas a rectangular cross-sectional shape whose top surface and bottomsurface have the same width, the present disclosure is not limitedthereto. For example, the width of the top surface of each of the lightemitting elements LE may be greater than the width of the bottom surfacethereof. That is, each of the light emitting elements LE may have atrapezoidal cross-sectional shape. In this case, because the area of theactive layer MQW of each of the light emitting elements LE increases,the amount of light emitted from each of the light emitting elements LEmay increase.

The common electrode layer CEL may be located on the light emittingelements LE. The common electrode layer CEL may be connected as onecommon layer to the second semiconductor layer SEM2 of each of the lightemitting elements LE.

The common electrode layer CEL may be an n-type semiconductor containingthe same material as that of the second semiconductor layer SEM2. Thecommon electrode layer CEL may include a semiconductor material having achemical formula of AlxGayIn1−x−yN (0≤x≤1, 0≤y≤1, 0≤x+y≤1). For example,it may be any one or more of n-type doped AlGaInN, GaN, AlGaN, InGaN,AlN, and InN. The common electrode layer CEL may be doped with an n-typedopant, and the n-type dopant may be Si, Ge, Sn, or the like. Forexample, the common electrode layer CEL may be n-GaN doped with n-typeSi.

Meanwhile, although FIG. 3 illustrates that the common electrode layerCEL is made of the same material as that of the second semiconductorlayer SEM2 and is integrated with the second semiconductor layer SEM2,the present disclosure is not limited thereto. In some embodiments, thecommon electrode layer CEL may be made of a material that is differentfrom that of the second semiconductor layer SEM2. That is, the commonelectrode layer CEL may be formed as a separate layer integrated withthe second semiconductor layer SEM2, and may be electrically connectedto the second semiconductor layer SEM2.

Each of the first connection electrodes CNE1 may be located between alight emitting element LE corresponding thereto and a correspondingpixel electrode AE in the display area DA. Each of the first connectionelectrodes CNE1 may be in contact with one surface of the firstsemiconductor layer SEM1 of a light emitting element LE correspondingthereto. Each of the first connection electrodes CNE1 may be in contactwith one surface of a pixel electrode AE corresponding thereto. Each ofthe first connection electrodes CNE1 may transmit the pixel voltageapplied to the pixel electrode AE to the light emitting element LE. Thewidth of the first connection electrode CNE1 may be less than the widthof the light emitting element LE, but the present disclosure is notlimited thereto.

The first connection electrode CNE1 may serve as a bonding metal forbonding the pixel electrode AE and the light emitting element LE to eachother during a manufacturing process. The first connection electrodeCNE1 may contain a material that may be electrically connected to thepixel electrode AE and the light emitting element LE. For example, thefirst connection electrode CNE1 may contain at least one of gold (Au),copper (Cu), aluminum (Al), or tin (Sn), or a transparent conductiveoxide such as indium tin oxide (ITO) or indium zinc oxide (IZO).Alternatively, the first connection electrode CNE1 may include a firstlayer containing any one of gold (Au), copper (Cu), aluminum (Al), andtin (Sn), and a second layer containing another one of gold (Au), copper(Cu), aluminum (Al), and tin (Sn).

The second connection electrode CNE2 may be connected to a commonelectrode connection portion CVS corresponding thereto. The secondconnection electrode CNE2 may be located on the common electrodeconnection portion CVS. The second connection electrode CNE2 may extendin the third direction DR3, and may be connected to the common electrodelayer CEL. The height of the second connection electrode CNE2 may besubstantially the same as the sum of the height of the light emittingelement LE and the height of the first connection electrode CNE1.

The second connection electrode CNE2 may contain a material that may beelectrically connected to the common electrode connection portion CVS.The second connection electrode CNE2 may be made of the same material asthat the first connection electrode CNE1. For example, the secondconnection electrode CNE2 may contain at least one of gold (Au), copper(Cu), aluminum (Al), or tin (Sn). Alternatively, the second connectionelectrode CNE2 may include a first layer containing any one of gold(Au), copper (Cu), aluminum (Al), and tin (Sn), and a second layercontaining another one of gold (Au), copper (Cu), aluminum (Al), and tin(Sn).

The second semiconductor layers SEM2 of the light emitting elements LEmay be electrically connected to each other through the common electrodelayer CEL. For example, the common electrode layer CEL may contain thesame material as that of the second semiconductor layer SEM2, and thesecond semiconductor layer SEM2 of each of the light emitting elementsLE may be integrally formed with the common electrode layer CEL. Thatis, the second semiconductor layer SEM2 of each of the light emittingelements LE may protrude from the common electrode layer CEL. The secondsemiconductor layers SEM2 may be spaced apart from each other.

The common electrode layer CEL may be electrically connected to thecommon electrode connection portion CVS of the semiconductor circuitboard 101 through the second connection electrode CNE2 located in thecommon electrode areas CPA1 and CPA2. Accordingly, the common electrodelayer CEL may receive the common voltage through the common electrodeconnection portion CVS of the semiconductor circuit board 101.

As shown in FIG. 3 , each of the plurality of pixels PX of the displaypanel 100 includes the light emitting element LE that emits any one ofthe first light, the second light, and the third light depending on thecurrent density, so that various colors may be displayed without awavelength conversion layer.

FIG. 4 is a diagram illustrating the band gap of the active layer of alight emitting element in the case of applying a driving current havinga first current density. FIG. 5 is a diagram illustrating the band gapof the active layer of a light emitting element in the case of applyinga driving current having a second current density.

Referring to FIGS. 4 and 5 , the active layer MQW of the light emittingelement LE may be made of InGaN having an indium (In) content of about30% to about 45%. In this case, the light emitted from the lightemitting element LE may be shifted from red to blue depending on thecurrent density. For example, as the current density increases, the bandgap of the active layer MQW of the light emitting element LE may bechanged from a rectangular shape, as shown in FIG. 4 , to a trapezoidalor parallelogram shape, as shown in FIG. 5 , due to a quantum-confinedstark effect (QCSE). In this case, the band filling in which carriersfill the quantum well of the active layer MQW is faster when the bandgap has a trapezoidal or parallelogram shape, as shown in FIG. 5 , thanwhen the band gap has a rectangular shape, as shown in FIG. 4 , so thatelectrons and holes may be recombined at a higher energy level when theband gap has the trapezoidal shape. Therefore, as the current densityapplied to the active layer MQW of the light emitting element LEincreases, the active layer MQW of the light emitting element LE mayemit light of a short wavelength. As the current density applied to theactive layer MQW of the light emitting element LE decreases, the activelayer MQW of the light emitting element LE may emit light of a longwavelength.

As described above, when the active layer MQW of the light emittingelement LE is made of InGaN having an indium (In) content of about 30%to about 45%, the active layer MQW may be controlled to emit shortwavelength light and long wavelength light by adjusting the currentdensity of the driving current applied to the active layer MQW. That is,in order to allow the light emitting element LE to emit the first lightthat is the long wavelength light, a driving current Ids having a firstcurrent density may be applied to the light emitting element LE. Toallow the light emitting element LE to emit the second light, a drivingcurrent Ids having a second current density, which is higher than thefirst current density, may be applied to the light emitting element LE.To allow the light emitting element LE to emit the third light that isthe short wavelength light, a driving current Ids having a third currentdensity, which is higher than the second current density, may be appliedto the light emitting element LE.

FIG. 6 is a waveform diagram illustrating a driving current according toone or more embodiments. FIG. 6 shows the driving current Ids applied tothe light emitting element LE during one frame period. FIG. 6 shows thedriving current Ids applied to the light emitting element LE in each ofthe case where the pixel PX expresses a peak white grayscale, the casewhere the pixel PX expresses a grayscale, the case where the pixel PXemits red light, the case where the pixel PX emits green light, and thecase where the pixel PX emits blue light. The peak white grayscaleindicates the brightest grayscale that may be expressed by the pixel PX.

Referring to FIG. 6 , one frame period may include a first period EP1, asecond period EP2, and a third period EP3. Although FIG. 6 illustratesthat the first period EP1, the second period EP2, and the third periodEP3 are arranged in the order of third period EP3, the second periodEP2, and the first period EP1 in one frame period, the presentdisclosure is not limited thereto.

The driving current Ids may be time-divided and applied to the lightemitting element LE during one frame period. For example, the drivingcurrent Ids may be applied to the light emitting element LE at the firstcurrent density during the first period EP1, may be applied to the lightemitting element LE at the second current density during the secondperiod EP2, and may be applied to the light emitting element LE at thethird current density during the third period EP3. The length of thefirst period EP1, the length of the second period EP2, and the length ofthe third period EP3 may be adjusted depending on to the grayscaleexpressed by the pixel PX. For example, when the pixel PX expresses thepeak white grayscale, the length of the first period EP1, the length ofthe second period EP2, and the length of the third period EP3 may belonger than those when the pixel PX expresses the grayscale. As thepixel PX expresses the peak white grayscale, the length of the firstperiod EP1, the length of the second period EP2, and the length of thethird period EP3 may increase, and as the pixel PX expresses the peakblack grayscale, the length of the period EP1, the length of the secondperiod EP2, and the length of the third period EP3 may decrease. Thepeak black grayscale indicates the darkest grayscale that may beexpressed by the pixel PX.

When the pixel PX emits red light, the driving current Ids may beapplied at the first current density only during the first period EP1.Further, when the pixel PX emits green light, the driving current Idsmay be applied at the second current density only during the secondperiod EP2. Further, when the pixel PX emits blue light, the drivingcurrent Ids may be applied at the third current density only during thethird period EP3.

Because the second current density is higher than the first currentdensity, and because the third current density is higher than the secondcurrent density, when the pixel PX expresses the peak white grayscale,the length of the first period EP1 may be longer than the length of thesecond period EP2, and the length of the second period EP2 may be longerthan the period of the third period EP3.

Because the current density of the driving current Ids increases as thepeak current value of the driving current Ids increases, a second peakcurrent value Ipeak2 of the driving current Ids may be higher than(e.g., greater than) a first peak current value Ipeak1. Further, a thirdpeak current value Ipeak3 of the driving current Ids may be higher than(e.g., greater than) the second peak current value Ipeak2.

As described above, when the active layer MQW of the light emittingelement LE is made of InGaN having an indium (In) content of about 30%to about 45%, the light emitting element LE may perform time division toemit the first light, the second light, and the third light byperforming time division on the driving current Ids applied to theactive layer MQW, and by applying the driving current Ids to the lightemitting element LE.

FIG. 7 is a waveform diagram illustrating a driving current applied to alight emitting element according to one or more other embodiments.

The embodiments corresponding to FIG. 7 are different from theembodiments corresponding to FIG. 6 in that the driving current Ids isapplied to the light emitting element LE over a plurality of firstemission periods EP1′, a plurality of second emission periods EP2′, anda plurality of third emission periods EP3′ during one frame period. InFIG. 7 , differences from the embodiments corresponding to FIG. 6 willbe mainly described.

Referring to FIG. 7 , one frame period may include R (R being a positiveinteger of 2 or more) first emission periods EP1′, Q (Q being a positiveinteger of 2 or more) second emission periods EP2′, and P (P being apositive integer of 2 or more) third emission periods EP3′. The lengthsof the R first periods EP1′ may be substantially the same. The lengthsof the Q second emission periods EP2′ may be substantially the same. Thelengths of the P third emission periods EP3′ may be substantially thesame.

The length of the first period EP1′, the length of the second periodEP2′, and the length of the third period EP3′ may be adjusted dependingon the grayscale expressed by the pixel PX. For example, when the pixelPX expresses the peak white grayscale, the length of the first periodEP1′, the length of the second period EP2′, and the length of the thirdperiod EP3′ may be longer than those when the pixel PX expresses thegrayscale. As the pixel PX expresses the peak white grayscale, thelength of the first period EP1′, the length of the second period EP2′,and the length of the third period EP3′ may increase, and as the pixelPX expresses the peak black grayscale, the length of the first periodEP1′, the length of the second period EP2′, and the length of the thirdperiod EP3′ may decrease.

When the pixel PX emits red light, the driving current Ids may beapplied at the first current density only during the R first periodsEP1′. Further, when the pixel PX emits green light, the driving currentIds may be applied at the second current density only during the Qsecond periods EP2′. Further, when the pixel PX emits blue light, thedriving current Ids may be applied at the third current density onlyduring the P third periods EP3′.

Because the second current density is higher than the first currentdensity, and because the third current density is higher than the secondcurrent density, when the pixel PX expresses the peak white grayscale,the length of the first period EP1′ may be longer than the length of thesecond period EP2′, and the length of the second period EP2′ may belonger than the length of the third period EP3′. Further, when the pixelPX expresses the peak white grayscale, during one frame period, the sumof the R first periods EP1′ may be longer than the sum of the Q secondperiods EP2′, and the sum of the Q second periods EP2′ may be longerthan the sum of the P third periods EP3′.

FIG. 8 is a flowchart illustrating a method for fabricating a displaydevice according to one or more embodiments. FIGS. 9 to 15 arecross-sectional views illustrating a method for fabricating a displaydevice according to one or more embodiments.

Hereinafter, a method for fabricating a display device according to oneor more embodiments will be described in detail with reference to FIGS.8 to 15 .

First, as shown in FIG. 9 , an undoped semiconductor layer USEM isformed on a second substrate 210, and the common electrode layer CEL isformed on the undoped semiconductor layer USEM (operation S110 in FIG. 8).

The second substrate 210 may be a sapphire substrate (Al₂O₃) or asilicon wafer containing silicon. However, the second substrate 210 isnot limited thereto, and may be a semiconductor substrate such as a GaAssubstrate or the like. Hereinafter, the case where the second substrate210 is a sapphire substrate will be described as an example.

The undoped semiconductor layer USEM may include an undopedsemiconductor, and may be a material that is not doped with an n-typedopant or p-type. For example, the undoped semiconductor layer USEM maybe at least one of undoped InAlGaN, GaN, AlGaN, InGaN, AlN, or InN, butthe present disclosure is not limited thereto. Although FIG. 13illustrates that a single undoped semiconductor layer USEM is formed onthe second substrate 210, the present disclosure is not limited thereto,and a plurality of undoped semiconductor layers USEM may be formed onthe second substrate 210 in other embodiments. The undoped semiconductorlayer USEM may be located to reduce a lattice constant differencebetween the common electrode layer CEL and the second substrate 210.

The common electrode layer CEL may include an n-type semiconductor. Forexample, the common electrode layer CEL may be any one or more of n-typedoped AlGaInN, GaN, AlGaN, InGaN, AlN, and InN.

The undoped semiconductor layer USEM and the common electrode layer CELmay be formed by an epitaxial growth method. The epitaxial growth methodmay be electron beam deposition, physical vapor deposition (PVD),chemical vapor deposition (CVD), plasma laser deposition (PLD),dual-type thermal evaporation, sputtering, metal organic chemical vapordeposition (MOCVD), or the like. For example, it may be performed by themetal organic chemical vapor deposition (MOCVD), but the presentdisclosure is not limited thereto.

Typically, a precursor material for forming the plurality ofsemiconductor material layers may be selected to form a target materialin a typically selectable range without any limitation. For example, theprecursor material may be a metal precursor including an alkyl groupsuch as a methyl group or an ethyl group. Examples of the precursormaterial may include, but are not limited to, trimethylgallium Ga(CH₃)₃,trimethylaluminum Al(CH₃)₃, and triethyl phosphate (C₂H₅)₃PO₄.

Second, as shown in FIG. 10 , a hard mask HM is formed on the commonelectrode layer CEL (operation S120 in FIG. 8 ).

The hard mask HM may be located on the entire common electrode layerCEL. The hard mask HM may contain an insulating material such as siliconoxide (SiO_(x)), silicon nitride (SiN_(x)), or silicon oxynitride(SiO_(x)N_(y)). The hard mask HM may function as a mask in a process forforming the light emitting elements LE.

Third, as shown in FIG. 11 , the hard mask HM is etched to form aplurality of openings OP exposing the common electrode layer CEL(operation S130 in FIG. 8 ).

The plurality of openings OP may be formed to be spaced apart from eachother. The gap and width of the plurality of openings OP may be set inconsideration of the arrangement and width of the light emittingelements LE.

In one or more embodiments in the drawing, a separate mask may belocated on the hard mask HM excluding the region where a plurality offirst openings OP1 will be formed, and the plurality of first openingsOP1 may be formed by performing wet etching or dry etching of the hardmask HM.

Fourth, as shown in FIG. 12 , the first light emitting elements LE1 areformed in the plurality of openings OP1 (operation S140 in FIG. 8 ).

The process of forming the light emitting elements LE may be performedby an epitaxial growth method. When the top surface of the commonelectrode layer CEL is exposed by the plurality of openings OP, asemiconductor crystal is grown by injecting a precursor material ontothe common electrode layer CEL. The second semiconductor layer SEM2 ofeach of the light emitting elements LE located on the common electrodelayer CEL may contain substantially the same material as that of thecommon electrode layer CEL, and may be formed by the growth of thesemiconductor crystal of the common electrode layer CEL. Accordingly,the second semiconductor layer SEM2 of each of the light emittingelements LE and the common electrode layer CEL may be integrated.

Then, the superlattice layer SLT, the active layer MQW, the electronblocking layer EBL, and the first semiconductor layer SEM1 aresequentially grown to complete the light emitting elements LE.

Fifth, as shown in FIG. 13 , the hard mask HM is etched, firstsub-connection electrodes SCNE1 are respectively formed on the lightemitting elements LE, a second sub-connection electrode SCNE2 is formedon the common electrode layer CEL, and third sub-connection electrodesSCNE3 are respectively formed on the pixel electrodes AE and the commonelectrode connection portions CVS of the semiconductor circuit board 101(operation S150 in FIG. 8 ).

The hard mask HM may be etched at one time by an etching process. Theetching process may be dry etching, wet etching, reactive ion etching(RIE), deep reactive ion etching (DRIE), inductively coupled plasmareactive ion etching (ICP-RIE), or the like.

Then, the first sub-connection electrode SCNE1 may be formed on the topsurface of the first semiconductor layer SEM1 of each of the lightemitting elements LE by a photolithography process.

Further, the second sub-connection electrode SCNE2 may be formed on thecommon electrode layer CEL by the photolithography process.

Furthermore, the third sub-connection electrodes SCNE3 may berespectively formed on the pixel electrodes AE and the common electrodeconnection portions CVS of the semiconductor circuit board 101 by thephotolithography process.

The first sub-connection electrodes SCNE1, the second sub-connectionelectrode SCNE2, and the third sub-connection electrodes SCNE3 may serveas a bonding metal. For example, the first sub-connection electrodesSCNE1, the second sub-connection electrode SCNE2, and the thirdsub-connection electrodes SCNE3 may contain at least one of gold (Au),copper (Cu), aluminum (Al), or tin (Sn), or may contain a transparentconductive oxide such as indium tin oxide (ITO) or indium zinc oxide(IZO).

Sixth, as shown in FIG. 14 , the first sub-connection electrodes SCNE1and the second sub-connection electrode SCNE2 are respectively bondedwith the third sub-connection electrodes SCNE3 to adhere the secondsubstrate 210 to a semiconductor circuit board 101 (operation S160 inFIG. 8 ).

The first sub-connection electrodes SCNE1 of the second substrate 210may be aligned to correspond to the pixel electrodes AE of thesemiconductor circuit board 101, respectively. Further, the secondsub-connection electrode SCNE2 of the second substrate 210 may bealigned to correspond to the common electrode connection portion CVS ofthe semiconductor circuit board 101. That is, the first sub-connectionelectrodes SCNE1 of the second substrate 210 may overlap the pixelelectrodes AE of the semiconductor circuit board 101 in the thirddirection DR3, respectively. The second sub-connection electrode SCNE2of the second substrate 210 may overlap the common electrode connectionportions CVS of the semiconductor circuit board 101 in the thirddirection DR3.

Then, the first sub-connection electrodes SCNE1 and the secondsub-connection electrode SCNE2 of the second substrate 210 are broughtinto contact with the respective third sub-connection electrodes SCNE3of the semiconductor circuit board 101. Then, respective ones of thefirst sub-connection electrodes SCNE1, the second sub-connectionelectrode SCNE2, and the third sub-connection electrodes SCNE3 arefusion-bonded at a temperature (e.g., a predetermined temperature).Accordingly, the second substrate 210 may be adhered to thesemiconductor circuit board 101.

Seventh, as shown in FIG. 15 , the second substrate 210 is removed, andthe undoped semiconductor layer USEM is etched (operation S170 in FIG. 8).

The second substrate 210 may be separated from the undoped semiconductorlayer USEM by a laser lift-off process. Alternatively, the secondsubstrate 210 may be removed by a polishing process, such as a chemicalmechanical polishing (CMP) process and/or an etching process.

The undoped semiconductor layer USEM may be removed by the polishingprocess, such as the CMP process, or may be removed by wet etching ordry etching. When the undoped semiconductor layer USEM is removed, apart of the common electrode layer CEL may be removed.

As described above, the pixel PX includes the light emitting element LEthat emits any one of the first light, the second light, and the thirdlight depending on the current density. Accordingly, it is possible tosimplify the manufacturing process, and to reduce the manufacturing costcompared to the case of separately forming the first light emittingelements that emit the first light, the second light emitting elementsthat emit the second light, and the third light emitting elements thatemit the third light.

FIG. 16A is a layout diagram illustrating another example of area A ofFIG. 1 .

The embodiments corresponding to FIG. 16A are different from theembodiments corresponding to FIG. 2 in that each of the plurality ofpixels PX includes the first light emitting element LE1 and a secondlight emitting element LE2. The description being made with reference toFIG. 16A is mainly directed to the differences from the embodimentscorresponding to FIG. 2 .

Referring to FIG. 16A, the first light emitting element LE1 may emit thefirst light and the second light depending on the current density of thedriving current applied thereto. The second light emitting element LE2may emit the third light.

In each of the plurality of pixels PX, the first light emitting elementLE1 and the second light emitting element LE2 may be arranged in thefirst direction DR1 as shown in FIG. 16A, but the present disclosure isnot limited thereto. In one or more embodiments, in each of theplurality of pixels PX, the first light emitting element LE1 and thesecond light emitting element LE2 may be arranged in the seconddirection DR2, or may be arranged in a diagonal direction between thefirst direction DR1 and the second direction DR2.

The first light emitting elements LE1 and the second light emittingelements LE2 may be alternately located in the first direction DR1. Thefirst light emitting elements LE1 may be arranged in the seconddirection DR2, and the second light emitting elements LE2 may bearranged in the second direction DR2, but the present disclosure is notlimited thereto.

FIG. 16A illustrates that each of the first light emitting elements LE1and the second light emitting elements LE2 has a circular planar shape,but the present disclosure is not limited thereto. In one or moreembodiments, each of the first light emitting elements LE1 and thesecond light emitting elements LE2 may have a polygonal shape such as atriangular shape, a quadrilateral shape, a pentagonal shape, a hexagonalshape, and an octagonal shape, an elliptical shape, or an atypicalshape. Further, the planar shape of the first light emitting element LE1and the planar shape of the second light emitting element LE2 may bedifferent from each other.

Further, as shown in FIG. 16A, when the luminous efficiency of the firstlight emitting element LE1 is lower than (e.g., less than) that of thesecond light emitting element LE2, the area of the first light emittingelement LE1 may be larger than the area of the second light emittingelement LE2, but the present disclosure is not limited thereto. In oneor more embodiments, when the luminous efficiency of the first lightemitting element LE1 is similar to that of the second light emittingelement LE2, as shown in FIG. 16B, the area of the first light emittingelement LE1 and the area of the second light emitting element LE2 may besubstantially the same. When the light emitting elements LE1 and LE2have substantially the same area, the light emitting elements LE1 andLE2 may be formed with a more uniform quality, and the manufacturingprocess may be facilitated. Alternatively, in one or more embodiments,when the luminous efficiency of the second light emitting element LE2 islower than (e.g., less than) that of the first light emitting elementLE1, the area of the second light emitting element LE2 may be greaterthan the area of the first light emitting element LE1.

FIG. 17 is a cross-sectional view illustrating an example of a displaypanel taken along line B-B′ of FIG. 16A.

The embodiments corresponding to FIG. 17 are different from theembodiments corresponding to FIG. 3 in that the first light emittingelement LE1 includes a first active layer MQW1, whereas the second lightemitting element LE2 includes a second active layer MQW2. In FIG. 17 ,differences from the embodiments corresponding to FIG. 3 will be mainlydescribed.

The first light emitting element LE1 may include the first semiconductorlayer SEM1, the electron blocking layer EBL, the first active layerMQW1, the superlattice layer SLT, and the second semiconductor layerSEM2, and the second light emitting element LE2 may include the firstsemiconductor layer SEM1, the electron blocking layer EBL, the secondactive layer MQW2, the superlattice layer SLT, and the secondsemiconductor layer SEM2. Because the first semiconductor layer SEM1,the electron blocking layer EBL, the superlattice layer SLT, and thesecond semiconductor layer SEM2 are substantially the same as thosedescribed with reference to FIG. 3 , a description thereof will beomitted.

When the active layers MQW1 and MQW2 are made of InGaN, the color oflight emitted from the active layers MQW1 and MQW2 may vary depending onthe content of indium (In). For example, as the content of indium (In)increases, the wavelength band of the light emitted from the activelayer is shifted to the red wavelength band, and as the content ofindium (In) decreases, the wavelength band of the light emitted from theactive layer may be shifted to the blue wavelength band.

The content of indium (In) in the first active layer MQW1 may be higherthan the content of indium (In) in the second active layer MQW2. Forexample, the content of indium (In) in the first active layer MQW1 maybe about 30% to about 45%, and the content of indium (In) in the secondactive layer MQW2 may be about 10% to 20%. In this case, the firstactive layer MQW1 may emit the first light or the second light dependingon the current density, and the second active layer MQW2 may emit thethird light.

As shown in FIG. 17 , each of the plurality of pixels PX of the displaypanel 100 includes the first light emitting element LE1 that emits anyone of the first light and the second light depending on the currentdensity, and the second light emitting element LE2 that emits the thirdlight, so that various colors may be displayed without the wavelengthconversion layer.

FIG. 18 is a waveform diagram illustrating a first driving current and asecond driving current according to one or more embodiments.

FIG. 18 illustrates a first driving current Ids1 applied to the lightemitting element LE during one frame period. FIG. 18 shows the firstdriving current Ids1 applied to the light emitting element LE in each ofthe case where the pixel PX expresses the peak white grayscale, the casewhere the pixel PX expresses the grayscale, the case where the pixel PXemits the red light, and the case where the pixel PX emits the greenlight. The peak white grayscale indicates the brightest grayscale thatmay be expressed by the pixel PX.

Referring to FIG. 18 , one frame period may include a first period EP1″and a second period EP2″. Although FIG. 18 illustrates that the firstperiod EP1″ and the second period EP2″ are arranged in the order of thesecond period EP2″ and the first period EP1″ in one frame period, butthe present disclosure is not limited thereto.

The first driving current Ids1 may be time-divided and applied to thelight emitting element LE during one frame period. For example, thefirst driving current Ids1 may be applied to the first light emittingelement LE1 at the first current density during the first period EP1″,and may be applied to the first light emitting element LE1 at the secondcurrent density during the second period EP2″. The length of the firstperiod EP1″ and the length of the second period EP2″ may be adjusteddepending on the grayscale expressed by the pixel PX. For example, whenthe pixel PX expresses the peak white grayscale, the length of the firstperiod EP1″ and the length of the second period EP2″ may be longer thanthose when the pixel PX expresses the grayscale. For example, as thepixel PX expresses the peak white grayscale, the length of the firstperiod EP1″ and the length of the second period EP2″ may increase, andas the pixel PX expresses the peak black grayscale, the length of thefirst period EP1″ and the length of the second period EP2″ may decrease.

When the pixel PX emits the red light, the first driving current Ids1may be applied at the first current density only during the first periodEP1″. Further, when the pixel PX emits the green light, the firstdriving current Ids1 may be applied at the second current density onlyduring the second period EP2″. Further, because the second currentdensity is higher than the first current density, when the pixel PXexpresses the peak white grayscale, the length of the first period EP1may be longer than the length of the second period EP2.

Because the current density of the driving current Ids increases as thepeak current value of the driving current Ids increases, the second peakcurrent value Ipeak2 of the driving current Ids may be higher than thefirst peak current value Ipeak1.

Meanwhile, the second light emitting element LE2 may emit lightdepending on the second driving current. The grayscale expression of thesecond light emitting element LE2 may be similar to that of the firstlight emitting element LE1. For example, the second driving currenthaving the third current density may be applied to the second lightemitting element LE2 during one frame period. The length of the periodin which the second driving current is applied may be adjusted dependingon the grayscale to be expressed by the pixel PX. For example, when thepixel PX expresses the peak white grayscale, the length of the period inwhich the second driving current is applied may be longer than that whenthe pixel PX expresses the grayscale. The length of the period in whichthe second driving current is applied may increase as the pixel PXexpresses the peak white grayscale, and the length of the period inwhich the second driving current is applied may increase as the pixel PXexpresses the peak black grayscale.

Alternatively, the grayscale of the second light emitting element LE2may be adjusted depending on the current density of the second drivingcurrent. For example, the second light emitting element LE2 may expressthe grayscale close to the peak white grayscale as the third currentdensity of the second driving current increases, and may express thegrayscale close to the peak black grayscale as the third current densityof the second driving current decreases.

As described above, when the first active layer MQW1 of the firstlight-emitting element LE1 is made of InGaN having an indium (In)content of about 30% to about 45%, the first light emitting element LE1may perform time division to emit the first light and the second lightby performing time division on the driving current Ids1 applied to thefirst active layer MQW1, and by applying it the first light emittingelement LE1.

FIG. 19 is a waveform diagram illustrating a first driving current and asecond driving current according to one or more other embodiments.

The embodiments corresponding to FIG. 19 are different from theembodiments corresponding to FIG. 18 in that the first driving currentIds is applied to the first light emitting element LE1 over a pluralityof first emission periods EP1′″ and a plurality of second emissionperiods EP2′″ during one frame period. In FIG. 19 , the differences fromthe embodiments corresponding to FIG. 18 will be mainly described.

Referring to FIG. 19 , one frame period may include R first emissionperiods EP1′″ and Q second emission periods EP2′″. The lengths of the Rfirst periods EP1′″ may be substantially the same. The lengths of the Qsecond emission periods EP2′″ may be substantially the same.

The length of the first period EP1′″ and the length of the second periodEP2′″ may be adjusted depending on the grayscale expressed by the pixelPX. For example, when the pixel PX expresses the peak white grayscale,the length of the first period EP1′″ and the length of the second periodEP2′″ may be longer than those when the pixel PX expresses thegrayscale. The length of the first period EP1′″ and the length of thesecond period EP2′″ may increase as the pixel PX expresses the peakwhite grayscale, and may decrease as the pixel PX expresses the peakblack grayscale.

When the pixel PX emits the red light, the first driving current Ids1may be applied at the first current density only during the R firstperiods EP1′″. Further, when the pixel PX emits the green light, thefirst driving current Ids1 may be applied at the second current densityonly during the Q second periods EP2′″.

Because the second current density is higher than the first currentdensity, the length of the first period EP1′″ may be longer than thelength of the second period EP2′″ when the pixel PX expresses the peakwhite grayscale. Further, when the pixel PX expresses the peak whitegrayscale, the sum of the R first periods EP1′″ may be longer than thesum of the Q second periods EP2′″ during one frame period.

FIG. 20 is a flowchart illustrating a method for fabricating a displaydevice according to still one or more other embodiments. FIGS. 21 to 28are cross-sectional views illustrating a method for fabricating adisplay device according to one or more embodiments.

Hereinafter, a method for fabricating a display device according tostill one or more other embodiments will be described in detail withreference to FIGS. 20 to 28 .

Operations S210 and S220 of FIG. 20 are substantially the same asoperations S110 and S120 of FIG. 8 , respectively, so that a descriptionthereof will be omitted.

First, as shown in FIG. 21 , the hard mask HM is etched to form theplurality of first openings OP1 exposing the common electrode layer CEL(operation S230 in FIG. 20 ).

In one or more embodiments in the drawing, a separate mask is located onthe hard mask HM except the region where the plurality of first openingsOP1 will be formed, and the plurality of first openings OP1 may beformed by performing wet etching or dry etching of the hard mask HM.

The plurality of first openings OP1 may be formed to be spaced apartfrom each other. The gap and width of the plurality of first openingsOP1 may be set in consideration of the arrangement and width of thefirst light emitting elements LE1.

Then, as shown in FIG. 22 , the first light emitting elements LE1 areformed in the plurality of first openings OP1 (operation S240 in FIG. 20).

The process of forming the first light emitting elements LE1 may beperformed by the epitaxial growth method. When the top surface of thecommon electrode layer CEL is exposed by the plurality of first openingsOP1, a semiconductor crystal is grown by injecting a precursor materialonto the common electrode layer CEL. The second semiconductor layer SEM2of each of the first light emitting elements LE1 located on the commonelectrode layer CEL may contain substantially the same material as thatof the common electrode layer CEL, and may be formed by the growth ofthe semiconductor crystal of the common electrode layer CEL.Accordingly, the second semiconductor layer SEM2 of each of the firstlight emitting elements LE1 and the common electrode layer CEL may beintegrated.

Next, the superlattice layer SLT, the first active layer MQW1, theelectron blocking layer EBL, and the first semiconductor layer SEM1 aresequentially grown to complete the first light emitting elements LE1.

Then, as shown in FIG. 23 , a mask pattern MP covering the first lightemitting elements LE1 is formed (operation S250 in FIG. 20 ).

The mask pattern MP may be formed of an inorganic layer such as asilicon oxide layer (SiO₂), an aluminum oxide layer (Al₂O₃), or ahafnium oxide layer (HfO_(x)), but the present disclosure is not limitedthereto. The mask pattern MP may contain the same material as that ofthe hard mask HM.

The mask pattern MP may be a protective layer or a barrier layer forprotecting the first light emitting elements LE1. The mask pattern MPmay be located to cover each of the first light emitting elements LE1.Further, the mask pattern MP may be located to cover the entire topsurface of the hard mask HM.

Then, as shown in FIG. 24 , the hard mask HM is etched to form aplurality of second openings OP2 exposing the common electrode layer CEL(operation S260 in FIG. 20 ).

In one or more embodiments in the drawing, a separate mask is located onthe hard mask HM except the region where the plurality of secondopenings OP2 will be formed, and the plurality of second openings OP2may be formed by performing wet etching or dry etching of the hard maskHM.

The plurality of second openings OP2 may be formed to be spaced apartfrom each other. The gap and width of the plurality of second openingsOP2 may be set in consideration of the arrangement and width of thesecond light emitting elements LE2.

Thereafter, as shown in FIG. 25 , the second light emitting elements LE2are formed in the plurality of second openings OP2 (operation S270 ofFIG. 20 ).

The process of forming the second light emitting elements LE2 may beperformed by the epitaxial growth method. When the top surface of thecommon electrode layer CEL is exposed by the plurality of secondopenings OP2, a semiconductor crystal is grown by injecting a precursormaterial onto the common electrode layer CEL. The second semiconductorlayer SEM2 of each of the second light emitting elements LE2 located onthe common electrode layer CEL may contain substantially the samematerial as that of the common electrode layer CEL, and may be formed bythe growth of the semiconductor crystal of the common electrode layerCEL. Accordingly, the second semiconductor layer SEM2 of each of thesecond light emitting elements LE2 and the common electrode layer CELmay be integrated.

Next, the superlattice layer SLT, the second active layer MQW2, theelectron blocking layer EBL, and the first semiconductor layer SEM1 aresequentially grown to complete the second light emitting elements LE2.

Then, as shown in FIG. 26 , the hard mask HM and the mask pattern MP areetched, the first sub-connection electrodes SCNE1 are respectivelyformed on the light emitting elements LE1 and LE2, the secondsub-connection electrode SCNE2 is formed on the common electrode layerCEL, and the third sub-connection electrodes SCNE3 are respectivelyformed on the pixel electrodes AE and the common electrode connectionportions CVS of the semiconductor circuit board 101 (operation S280 inFIG. 20 ).

The hard mask HM and the mask pattern MP may be etched at one time bythe etching process. The etching process may be dry etching, wetetching, reactive ion etching (RIE), deep reactive ion etching (DRIE),inductively coupled plasma reactive ion etching (ICP-RIE), or the like.

Then, the first sub-connection electrode SCNE1 may be formed on the topsurface of the first semiconductor layer SEM1 of each of the lightemitting elements LE1 and LE2 by the photolithography process.

Further, the second sub-connection electrode SCNE2 may be formed on thecommon electrode layer CEL by the photolithography process.

Furthermore, the third sub-connection electrodes SCNE3 may berespectively formed on the pixel electrodes AE and the common electrodeconnection portions CVS of the semiconductor circuit board 101 by thephotolithography process.

The first sub-connection electrodes SCNE1, the second sub-connectionelectrode SCNE2, and the third sub-connection electrodes SCNE3 may serveas a bonding metal. For example, the first sub-connection electrodesSCNE1, the second sub-connection electrode SCNE2, and the thirdsub-connection electrodes SCNE3 may contain at least one of gold (Au),copper (Cu), aluminum (Al), or tin (Sn), or may contain a transparentconductive oxide such as indium tin oxide (ITO) or indium zinc oxide(IZO).

Then, as shown in FIG. 27 , the first sub-connection electrodes SCNE1and the second sub-connection electrode SCNE2 may be respectively bondedwith the third sub-connection electrodes SCNE3 to adhere the secondsubstrate 210 to the semiconductor circuit board 101 (operation S290 inFIG. 20 ).

The first sub-connection electrodes SCNE1 of the second substrate 210may be aligned to correspond to the pixel electrodes AE of thesemiconductor circuit board 101, respectively. Further, the secondsub-connection electrode SCNE2 of the second substrate 210 may bealigned to correspond to the common electrode connection portion CVS ofthe semiconductor circuit board 101. That is, the first sub-connectionelectrodes SCNE1 of the second substrate 210 may overlap the pixelelectrodes AE of the semiconductor circuit board 101 in the thirddirection DR3, respectively. The second sub-connection electrode SCNE2of the second substrate 210 may overlap the common electrode connectionportions CVS of the semiconductor circuit board 101 in the thirddirection DR3.

Then, the first sub-connection electrodes SCNE1 and the secondsub-connection electrode SCNE2 of the second substrate 210 arerespectively brought into contact with the third sub-connectionelectrodes SCNE3 of the semiconductor circuit board 101. Then, the firstsub-connection electrodes SCNE1, the second sub-connection electrodeSCNE2, and the third sub-connection electrodes SCNE3 are fusion-bondedat a temperature (e.g., a predetermined temperature). Accordingly, thesecond substrate 210 may be adhered to the semiconductor circuit board101.

Then, as shown in FIG. 28 , the second substrate 210 is removed, and theundoped semiconductor layer USEM is etched (operation S300 in FIG. 20 ).

The second substrate 210 may be separated from the undoped semiconductorlayer USEM by the laser lift-off process. Alternatively, the secondsubstrate 210 may be removed by a polishing process such as a chemicalmechanical polishing (CMP) process and/or an etching process.

The undoped semiconductor layer USEM may be removed by the polishingprocess such as the CMP process, or may be removed by wet etching or dryetching. When the undoped semiconductor layer USEM is removed, a part ofthe common electrode layer CEL may be removed.

As described above, the pixel PX includes the first light emittingelement LE1 that emits any one of the first light and the second lightdepending on the current density, and the second light emitting elementLE2 that emits the third light. Accordingly, it is possible to simplifythe manufacturing process, and to reduce the manufacturing cost comparedto the case of separately forming the first light emitting elements thatemit the first light, the second light emitting elements that emit thesecond light, and the third light emitting elements that emit the thirdlight.

FIG. 29 is a diagram illustrating a virtual reality device including adisplay device according to one or more embodiments. FIG. 29 illustratesa virtual reality device 1 to which a display device 10_1 according toone or more embodiments is applied.

Referring to FIG. 29 , the virtual reality device 1 according to one ormore embodiments may be a glass-type device. The virtual reality device1 according to one or more embodiments may include the display device10_1, a left lens 10 a, a right lens 10 b, a support frame 20, temples30 a and 30 b, a reflection member 40, and a display device storage 50.

Although FIG. 29 illustrates the virtual reality device 1 including thetemples 30 a and 30 b, the virtual reality device 1 according to one ormore embodiments may be applied to a head mounted display including ahead mounted band that may be worn on a head, instead of the temples 30a and 30 b. That is, the virtual reality device 1 according to one ormore embodiments is not limited to that shown in FIG. 29 , and may beapplied in various forms to various electronic devices.

The display device storage 50 may include the display device 10_1 andthe reflection member 40. The image displayed on the display device 10_1may be reflected by the reflection member 40 and may be provided to auser's right eye through the right lens 10 b. Accordingly, the user canview the virtual reality image displayed on the display device 10_1through the right eye.

Although FIG. 29 illustrates that the display device storage 50 islocated at the right end of the support frame 20, the present disclosureis not limited thereto. For example, the display device storage 50 maybe located at the left end of the support frame 20, and in this case,the image displayed on the display device 10_1 may be reflected by thereflection member 40 and provided to a user's left eye through the leftlens 10 a. Accordingly, the user can view the virtual reality imagedisplayed on the display device 10_1 through the left eye.Alternatively, the display device storage 50 may be located at both theleft end and the right end of the support frame 20. In that case, theuser can view the virtual reality image displayed on the display device10_1 through both the left eye and the right eye.

FIG. 30 is a diagram illustrating a smart device including a displaydevice according to one or more embodiments.

Referring to FIG. 30 , a display device 10_2 according to one or moreembodiments may be applied to a smart watch 2 that is one of the smartdevices.

FIG. 31 is a view illustrating a dashboard of an automobile and a centerfascia including a display device according to one or more embodiments.FIG. 31 illustrates a vehicle to which display devices 10_a, 10_b, 10_c,10_d, and 10_e according to one or more embodiments are applied.

Referring to FIG. 31 , the display devices 10_a, 10_b, and 10_caccording to one or more embodiments may be applied to the dashboard ofthe automobile, the center fascia of the automobile, or the centerinformation display (CID) of the dashboard of the automobile. Further,the display devices 10_d, and 10_e according to one or more embodimentsmay be applied to a room mirror display instead of side mirrors of theautomobile.

FIG. 32 is a diagram illustrating a transparent display device includinga display device according to one or more embodiments.

Referring to FIG. 32 , a display device 10_3 according to one or moreembodiments may be applied to the transparent display device. Thetransparent display device may display an image IM, and also maytransmit light. Thus, a user located on the front side of thetransparent display device can view an object RS or a background on orbehind the rear side of the transparent display device as well as theimage IM displayed on the display device 10_3. When the display device10_3 is applied to the transparent display device, the first substrate110 shown in FIG. 3 may include a light transmitting portion capable oftransmitting light or may be made of a material capable of transmittinglight.

However, the aspects of embodiments of the present disclosure are notlimited to the one set forth herein. The above and other aspects andfeatures of embodiments of the present disclosure will become moreapparent to one of daily skill in the art to which the presentdisclosure pertains by referencing the claims, with functionalequivalents thereof to be included therein.

What is claimed is:
 1. A display device comprising: a substrate; a pixelelectrode on the substrate; a light emitting element on the pixelelectrode; and a common electrode layer on the light emitting element,and configured to receive a common voltage, wherein the light emittingelement is configured to emit a first light according to a drivingcurrent having a first current density, is configured to emit a secondlight according to a driving current having a second current density,and is configured to emit a third light according to a driving currenthaving a third current density.
 2. The display device of claim 1,wherein one frame period comprises a first period, a second period, anda third period, and wherein the driving current is applied at the firstcurrent density during the first period, is applied at the secondcurrent density during the second period, and is applied at the thirdcurrent density during the third period.
 3. The display device of claim2, wherein, when the light emitting element emits light with a peakwhite grayscale, a length of the first period is longer than a length ofthe second period, and the length of the second period is longer than alength of the third period.
 4. The display device of claim 2, whereinthe first current density is less than the second current density, andwherein the first light has a longer wavelength than the second light.5. The display device of claim 2, wherein the second current density isless than the third current density, and wherein the second light has alonger wavelength than the third light.
 6. The display device of claim2, wherein the first light is light of a red wavelength band, the secondlight is light of a green wavelength band, and the third light is lightof a blue wavelength band.
 7. The display device of claim 2, wherein anactive layer of the light emitting element comprises InGaN having anindium (In) content of about 30% to about 45%.
 8. The display device ofclaim 2, wherein a first peak current value of the driving currentduring the first period is lower than a second peak current value of thedriving current during the second period.
 9. The display device of claim2, wherein a second peak current value of the driving current during thesecond period is lower than a third peak current value of the drivingcurrent during the third period.
 10. The display device of claim 2,wherein the first current density of the driving current is constantduring the first period, the second current density of the drivingcurrent is constant during the second period, and the third currentdensity of the driving current is constant during the third period. 11.The display device of claim 10, wherein the first period, the secondperiod, and the third period are adjusted according to a grayscale ofthe light emitting element.
 12. The display device of claim 1, whereinone frame period comprises R (R being an integer greater than or equalto 2) first periods, Q (Q being an integer greater than or equal to 2)second periods, and P (P being an integer greater than or equal to 2)third periods, and wherein the driving current is applied at the firstcurrent density during the first periods, is applied at the secondcurrent density during the second periods, and is applied at the thirdcurrent density during the third periods.
 13. The display device ofclaim 12, wherein, in the one frame period, a sum of the first periodsis longer than a sum of the second periods, and the sum of the secondperiods is longer than a sum of the third periods.
 14. A display devicecomprising: a substrate; pixel electrodes on the substrate; lightemitting elements respectively on the pixel electrodes; and a commonelectrode layer on the light emitting elements, and configured toreceive a common voltage, wherein each of the light emitting elementscomprises: a first light emitting element configured to emit a firstlight according to a first driving current having a first currentdensity, and configured to emit a second light according to a firstdriving current having a second current density; and a second lightemitting element configured to emit a third light according to a seconddriving current.
 15. The display device of claim 14, wherein one frameperiod comprises a first period and a second period, and wherein thedriving current is configured to be applied at the first current densityduring the first period, and is configured to be applied at the secondcurrent density during the second period.
 16. The display device ofclaim 15, wherein, when the first light emitting element emits lightwith a peak luminance, a length of the first period is longer than alength of the second period.
 17. The display device of claim 16, whereinthe first current density is less than the second current density, andthe first light has a longer wavelength than the second light.
 18. Thedisplay device of claim 14, wherein an area of the first light emittingelement is larger than an area of the second light emitting element. 19.The display device of claim 14, wherein an active layer of the firstlight emitting element comprises InGaN having an indium (In) content ofabout 30% to about 45%, and wherein an active layer of the second lightemitting element comprises InGaN having an indium (In) content of 10% to20%.
 20. A method for fabricating a display device, comprising: forminga common electrode layer on a substrate; forming a hard mask on thecommon electrode layer; etching the hard mask to form openings exposingthe common electrode layer; forming light emitting elements in theopenings, respectively; removing the hard mask; forming first connectionelectrodes on the light emitting elements, respectively; forming secondconnection electrodes on pixel electrodes of a semiconductor circuitboard, respectively; and bonding the first connection electrodes to thesecond connection electrodes, wherein an active layer of each of thelight emitting elements comprises InGaN having an indium (In) content ofabout 30% to about 45%.